Method of directional radio communication

ABSTRACT

A method of directional radio communication in a wireless communications network between a first station and a second station. The method comprises the steps of transmitting a plurality of communication bursts from the first station to the second station, each of the bursts being substantially continuous and comprising a reference signal having a plurality of reference signal components and a data signal having a plurality of data signal components wherein respective signal components of the reference signal are transmitted in substantially different directions, the data signal components being transmitted in the substantially different directions.

This invention relates to a method of directional radio communicationand in particular, but not exclusively, to a method of signal processingfor use in cellular communication networks using space division multipleaccess.

Cellular communication networks based on space division multiple accessand the advantages associated therewith are well known. The area coveredby a cellular network is divided into a plurality of cell or cellsectors. Each cell is served by a base station which transmits signalsto and receives signals from mobile stations located in the cell or cellsector associated with the respective base station. In a space divisionmultiple access system, the base transceiver station will not transmitsignals intended for a given mobile station throughout the cell or cellsector but will only transmit the signal in a beam direction from whicha signal from the mobile station is received.

As the beam which is transmitted by the base transceiver station mayonly be transmitted in a particular direction and accordingly may berelatively narrow, the transmission power is concentrated into thatnarrow beam. This results in a better signal to noise ratio with boththe signals transmitted from the base transceiver station and thesignals received by the base transceiver station. Additionally, as aresult of the directionality of the base transceiver station, animprovement in the signal to interference ratio of the signal receivedby the base transceiver station can be achieved. The interference causedby the signal transmitted by the base station to the mobile station toother mobile stations in the same cell or adjacent cells is alsoreduced. This increases the capacity of the system and/or increases thequality of communication.

SDMA systems can be implemented in analogue and digital cellularnetworks and may be incorporated in the various existing standards suchas GSM, DCS 1800, TACS, AMPS and NMT. SDMA systems can also be used inconjunction with other existing multiple access techniques based, forexample, on time division multiple access (TDMA), code division multipleaccess (CDMA), such as that described by the US IS-95 CDMA standard andthe proposed third generation standard, and frequency division multipleaccess (FDMA) techniques.

As is known, a signal from a mobile station will generally followseveral paths to the BTS. Those plurality of paths are generallyreferred to as multipaths. A given signal which is transmitted by themobile station may then be received by the base transceiver station frommore than one direction due to these multipath effects.

Signals transmitted from a mobile station to a base transceiver stationare known as “uplink” signals and signals transmitted from a basetransceiver station to a mobile station are known as “downlink” signals.The uplink communication stream received by the base transceiver stationfrom the mobile station comprises a series of communication burstsreceived in successive time slots. Each received burst of the uplinkcommunication stream includes a reference signal and a data signal andthese portions in turn each comprise a succession of signal componentsreferred to hereinafter as bits. Likewise, the downlink communicationstream transmitted from the base transceiver station to the mobilestation comprises a series of communication bursts transmitted insuccessive time slots. Each respective burst of the downlinkcommunication stream includes a reference signal and a data signal, eachof which in turn comprising a succession of signal components referredto hereinafter as bits. The reference signals of the uplink and downlinkcommunication streams are, in this example, referred to as pilot signalsto be consistent with CDMA terminology.

It has been proposed that Pilot signals transmitted from the mobilestation MS be used by the receiving base station to monitor the spatialproperties of the receive communication stream in order to determineoptimum transmission parameters. Conventional adaptive base transceiverstations process each communication burst received in the uplinkdirection to determine parameters for the corresponding burst in thedownlink direction. The direction of transmission to be used in thedownlink communication for a given time slot is determined based ondirection of arrival information estimated from the uplink communicationof the corresponding time slot, the uplink and downlink signals being atdifferent frequencies.

Circuitry within the base transceiver station determines, for eachreceive time slot, an angular power profile of the uplink signalimpinging on the base station antenna array from the mobile station andindicates transmission parameters to be used in each transmission timeslot. In practice, the determined angular power profile is supplied tosignal processing and decision circuitry which executes a beam selectionalgorithm to determine the downlink transmission parameters. Thus, thedirection of transmission for a given communication burst, including forthe pilot and data signals within that burst, is determined fromestimations of parameters of pilot symbols received from the mobilestation during the corresponding uplink communication burst and are keptfixed for at least the duration of that burst, i.e. for the entiretransmission time slot.

However, since the envelope of the signal received at the basetransceiver station will depend on the combination sum of a large numberof signals having phases related with their respective carrierfrequencies, it can be said that the short term responses (e.g.instantaneous behaviour) of the uplink and downlink channels will beuncorrelated. That is, the uplink and downlink channels are reciprocalonly in the long term. One result is that the channel and directions ofsignal arrival (DoA) estimated from the uplink do not correspond withthose required to communicate properly with the mobile station in thedownlink direction. This problem worsens in environments characterizedby larger angular spreads (e.g., micro-and pico-cells) and also when theangular resolution of base station is increased (e.g., the number ofantenna elements is large).

The performance of downlink is measured not only in terms of the qualityof signal registered at the receiving mobile station but also takinginto consideration the operative cost required to achieve that level ofquality. The base station aims to achieve at the mobile station a signalquality which is sufficient to produce an acceptable and/orpre-determined quality of service with minimum expenditure of resources.Spectral efficiency has direct impact on system capacity and linkperformance. Improving link performance will generally require anincrease in transmission power or increased use of diversity, which tendto increase the level of generated interference. The nature ofinterference is different from widely angular (e.g.,omnidirectional/sector antennas) to narrowly angular (e.g., adaptiveantennas). In the case of widely angular antennas, since the energy isevenly distributed over the whole cell/sector, the interference ischaracterized by a low angular density. Whereas in the case of angularlynarrow antennas, the interfering energy is concentrated in the narrowbeams used. In multi-rate systems proposed in wide band-CDMA standardswhere high-bit rate users transmit with correspondingly high powerlevels, the conventional use of adaptive antennas described hereinbeforewill produce highly coloured spatial interference.

Embodiments of the present invention seek to provide an improved methodfor directional radio communication.

According to an aspect of the present invention there is provided amethod of directional radio communication in a wireless communicationsnetwork between a first station and a second station, said methodcomprising the steps of transmitting a plurality of communication burstsfrom said first station to said second station, each of said burstsbeing substantially continuous and comprising a reference signal havinga plurality of reference signal components and a data signal having aplurality of data signal components wherein respective signal componentsof said reference and/or data signals are transmitted in substantiallydifferent directions.

Preferred methods improve link quality because they lead to improvementsin spatial correlations between the uplink and downlink channels.Preferred methods also provide fast angular diversity and the efficientwhitening of the generated co-channel interference. Methods embodyingthe invention have particular advantages in radio environmentscharacterised by large angular spreads and/or where base transceiverstations have relatively high angular resolutions.

A number of pilot and/or data signal transmission schemes may beemployed in various embodiments. In one embodiment, a number of pilotreference signal components are transmitted in different directions atdifferent times, consecutive reference signal components beingtransmitted in different directions and a number of said data signalcomponents are transmitted in different directions at different times,the order of directional transmission used corresponding to that usedduring transmission of said reference signal components.

In another embodiment, a number of pilot signal components aretransmitted in different directions at substantially the same time and anumber of said data signal components are transmitted in differentdirections at different times. This allows the data signal components tobe transmitted without regard to the order of directional transmissionused.

In another embodiment, a different spreading code is used fortransmission in each direction.

In another embodiment, the transmission of pilot signals is distributedthroughout the communication burst with sets of data signal componentsdisposed therebetween.

According to another aspect of the present invention there is provided atransceiver station for directional radio communication in a wirelesscommunications network between a first station and a second station,said transceiver station comprising means for transmitting a pluralityof communication bursts from said first station to said second station,each of said bursts being substantially continuous and comprising areference signal having a plurality of reference signal components and adata signal having a plurality of data signal components, said meansbeing operable to transmit respective signal components of saidreference signals in substantially different directions, the data signalcomponents being transmitted in said substantially different locations.

For a better understanding of the present invention and as to how thesame may be carried into effect, reference will be made by way ofexample only, to the accompanying drawings in which:g drawings in which:

FIG. 1 is a schematic view of a base transceiver station and itsassociated cell sectors;

FIG. 2 is a schematic view of the base transceiver station of FIG. 1;

FIG. 3 is a schematic illustration of a first embodiment of the methodof directional radio communication;

FIG. 4 is an example of direction of arrival data;

FIG. 5 is a more detailed representation of a downlink communicationburst used in a second embodiment;

FIG. 6 is a representation of a downlink communication burst used in athird embodiment of the method of directional radio communication;

FIG. 7 is a representation of a downlink communication burst used in afourth embodiment of the method of directional radio communication; and

FIG. 8 is a representation of a downlink communication burst used in afifth embodiment of the method directional radio communication.

Reference will first be made to FIG. 1 which shows three cell sectors 2of a cellular mobile telephone network. The three cell sectors 2 areserved by respective base transceiver stations (BTS) 4. Three separatebase transceiver stations 4 are provided at the same location. Each BTS4 has a transceiver which transmits and receives signals to and from arespective one of the three cell sectors 2. Thus, one dedicated basetransceiver station is provided for each cell sector 2. Each BTS 4 isthus able to communicate with mobile stations (MS) such as mobiletelephones which are located in respective cell sectors 2.

Data is transmitted between the BTS 4 and the MS in communicationbursts. The communication bursts include a reference signal which is aknown sequence of data. The purpose of the reference signal is generallyto allow information which assists operation of the system to beobtained. This type of information includes, for example, direction ofarrival information, signal strength information and delay information.In current GSM systems the reference signal is referred to as thetraining sequence, whereas in CDMA systems the reference signalcorresponds to the pilot signal.

Preferred embodiments will be described in the context of a codedivision multiple access system which uses an antenna array at the basestation. Each communication burst is transmitted in a givencommunication channel defined by the selected direction and the appliedspreading code.

FIG. 2 shows a schematic view of a base transceiver station 4 suitablefor code/space division multiple access systems. It should beappreciated that the various blocks illustrated in FIG. 2 do notnecessarily correspond to separate elements of an actual basetransceiver station for performing the method of the present invention.The various blocks illustrated in FIG. 2 correspond to various functionscarried out by the base transceiver station. The base transceiverstation 4 has an antenna array 6. The base station 4 only serves one ofthe three cell sectors 2 shown in FIG. 1. Another two base stations 4are provided to serve the other two cell sectors 2. In this example, theantenna array 6 has eight antenna elements. The elements are arranged tohave a spacing of about a half wavelength between each antenna elementand are arranged in a horizontal row in a straight line. Each antennaelement is arranged to transmit and receive signals and can have anysuitable construction. Each antenna element may be a dipole antenna, apatch antenna or any other suitable antenna. The eight antenna elementstogether define a phased antenna array 6.

As is known, each antenna element of the phased array antenna 6 issupplied with the same signal to be transmitted to a mobile station MS.However, the phases of the signals supplied to the respective antennaelements are shifted with respect to each other. The differences in thephase relationship between the signals supplied to the respectiveantenna elements gives rise to a directional radiation pattern. Theantenna array 6 can be controlled to provide a beam b₁-b₈ in one or moreof the eight directions illustrated. For example, the antenna array 6could be controlled to transmit a signal to a MS only in the directionof beam b₅ or only in the direction of beam b₆ or in more than one beamdirection at the same time. For example, a signal may be transmitted inthe two directions defined by beam b₅ and beam b₆.

FIG. 2 is only a schematic representation of the eight possible beamdirections which can be achieved with the antenna array 6. In practice,however, there will in fact be an overlap between adjacent beams. Insome embodiments of the present invention, the width of the beams can bevaried as well as the number of beams which are provided to cover agiven area.

The control and demodulation circuitry 8 includes beam forming circuitrysuch as Butler matrix circuitry, amplifier stages, analogue-to-digitalconverter arrays and digital to analogue converter arrays. In thereceive direction, the beam forming circuitry detects the phasedifference between each of the signals received by the respectiveantenna elements and uses this information to determine the or each beamdirection from which the signal has been received. Received signals aretypically then passed through the amplifier stages to demodulationcircuitry where the carrier frequency component is removed. The receivedanalogue signal is converted to a digital signal and is output to thesignal processing and decision circuitry 10. In the transmit direction,the relative phase of the signal supplied to each antenna element andthus also the desired beam direction is controlled by the beam formingcircuitry. Before being supplied to the antenna elements digital datafrom the signal processing circuitry are converted to analogue signalsand modulated onto the carrier frequency.

The signal processing and decision circuitry 10 removes the spreadingcodes from the received signal. The signal processing and decisioncircuitry determines the channel impulse response for the receivedsignals from which parameters used to define a channel for transmissionof subsequent signals can be determined. The signal processing anddecision circuitry 10 also carries out cross-correlation and analysis.Cross-correlation is used to generate taps which are representative ofthe channel impulse response for that correlation and compares receivedsignals and stored information. A channel impulse response is generatedfor each channel corresponding to a given communication burst receivedin each of the eight antenna directions b₁-b₈. A given communicationburst may be received in one or more beam directions.

The analysis carried out within the signal processing and decisioncircuitry 10 is for determining and storing the maximum energycalculated from the channel impulse response. The signal processing anddecision circuitry 10 also analyses the channel impulse responses toascertain the minimum delay with which a given signal is received Thechannel with the minimum delay may represent the line of sight pathbetween a mobile station and its base transceiver station.

Decision circuitry of the signal processing and decision circuitry 10compares the determined parameters for each channel to selecttransmission parameters for signals to be subsequently transmitted. Thedecision circuitry selects transmission parameters such as beamdirection and power level based on information from the receivedsignals. This selection can use simple methods for selection such asselecting the beam direction(s) having the maximum energy and minimumdelay in the received signals. Alternatively, more complicated methodsof selection may be used.

FIG. 3 schematically illustrates a bit level processing method for usein directional radio communication networks. As shown in FIG. 3, thebase transceiver station receives an uplink communication stream 30 froma mobile station MS. The uplink communication stream 30 comprises aseries of communication bursts in (i+1) th, ith and (i+1)th receive timeslots, respectively. Each communication burst includes a pilot signal Pand a data signal D, each of which in turn comprising a plurality ofsignal bits. The signal processing and decision circuitry 10 of the basetransceiver station 4 uses a beam selection algorithm 34 to determinetransmission directions for a given downlink communication time slotbased on the pilot signal received in the corresponding uplinkcommunication burst and possibly also taking into account informationfrom previous time slots 36.

For communication in the downlink direction the direction selected fortransmission is varied within the communication burst (i.e. within agiven time slot). For example, respective bits of the pilot signal Pand/or data signal D of the downlink communication burst are transmittedin different directions. This is schematically illustrated for the datasignal by the directional antenna lobes b₁, b₂ and b₃ of FIG. 3.Preferably, the direction of transmission is changed from bit to bit sothat the directions employed will thus repeat themselves in a cyclicalmanner. The total number of selectable beam directions may be apredetermined number. In FIG. 3, three directions are used in some ofthe time slots. The number of directions used may vary from time slot totime slot.

According to the general scheme of FIG. 3 the base transceiver station 4estimates an angular power profile upon reception of an uplinkcommunication burst and using this information determines the directionsof transmission to be used in the corresponding downlink communicationburst. This angular power profile is based on the pilot signals andincludes direction of arrival information, an example of which isprovided in FIG. 4. The power profile illustrated in FIG. 4 showsestimated signal power (above a given threshold Th) as a function ofantenna beam direction measured in azimuthal angle of arrival. Accordingto the angular power profile of FIG. 4, signals of appreciable strengthi.e. above the threshold Th are received simultaneously in the antennabeam directions b_(1, b) ₂ and b₃, with the signal of maximum energybeing received from direction b₃. The predetermined threshold Th is usedto ensure that only directions of arrival having appreciable signalstrengths are taken into account.

The base transceiver station 4 transmits a pilot signal P indicating thedirections of transmission to be used in the subsequent transmission ofthe data signal D of that communication burst. This allows the mobilestation MS to estimate the channel corresponding to each of thedirections of transmission to be used. In some embodiments, a pluralityof pilot signal components are transmitted simultaneously and in othersa pre-determined pilot transmission sequence is employed. The pilottransmission can be carried out by a number of different schemes. Datatransmission in the downlink direction involves, where ever possible,consecutive bits of the data signal being transmitted in differentdirections. Where a predetermined pilot transmission sequence isemployed, benefits from this type of directional hopping are maximisedif the directional transmission pattern employed in the transmission ofdata corresponds to that defined by the pilot signal components of thesame burst, as will be explained in more detail hereinafter.

The mobile station will have prior knowledge that the base transceiverstation 4 will use varying directions of transmission in the course of adownlink communication burst. In the method embodying the presentinvention bit level downlink processing of the signal to be transmittedtakes place. When the spatial and temporal granularity of thetransmitted signal is broken down to the bit level as described herein,gain is obtained not only in terms of diversity in the desired signal(bit level beam-hopping), but also from the interference standpoint. Themain advantages of this method are the improvement of the link qualityin the downlink direction and the increase of the system capacity.Preferred embodiments provide fast angular diversity and efficientlywhiten (randomize) the generated co-channel interference. The former isadvantageous in low mobility environments while the latter alleviatesthe effects of interference to other users by whitening the structure ofthe transmitted signal in the spatial and temporal domains.

According to a second embodiment illustrated in FIG. 5, an angular beamprofile such as that in FIG. 4 is established by the processing anddecision circuitry 10 of the base transceiver station 4 and the beamdirections b₁, b₂ and b₃ corresponding to the received directions b₁, b₂and b₃ are determined as the downlink directions of transmission for theith time-slot. Preferably, at least a component of pilot signal P is tobe transmitted in each of these directions. In this example, pilotsignal components are transmitted three times in the time slot. Thepilot signal bits or bit sequence P₁, P₂ and P₃ may be the same ordifferent. Preferably they are different. The pilot signal of the downlink communication burst comprises a first pilot signal bit P₁transmitted towards the first direction b₁, a second pilot signal bit P₂transmitted towards the second direction b₂ and a third pilot signal bitP₃ transmitted in the third direction b₃. The three pilot signal bitsP₁, P₂ and P₃ are thus transmitted consecutively. The receiving mobilestation uses the pilot signal bits of the communication burst toestimate the channel impulse response associated with each transmitteddirection. The data bits d₁, d₂ and d₃ of the ith time slot are thenrespectively transmitted in the corresponding directions b₁, b₂ and b₃.The predetermined transmission order of the pilot signal bits P₁, P₂ andP₃ defines a directional hopping pattern which is replicated duringtransmission of the data bits d₁, d₂ and d₃ of the same communicationburst. Successive data bits are transmitted in different directions.

This enables the mobile station MS to process each received data bitusing information obtained from the pilot signal received from the samerespective direction.

For simplicity and to minimise the use of overhead information, thenumber of transmitted pilot signals Np can be kept fixed from onecommunication burst to the next. For example, Np may equal 3. If thenumber of available directions of transmission exceeds the number ofpilot signal bits Np only the best Np directions are selected fordownlink transmission. Alternatively, if the number of availabledirections for transmission is lower than the number of pilot signalbits Np, some directions can be repeated in the transmission. In thiscase, the downlink transmission direction is varied such that the samedirection is not used for the transmission of consecutive data bits.

In this embodiment, the directions of transmission for the downlinkdirection are selected based on the energy of the corresponding receivedsignal in the uplink direction. However, as mentioned in relation to thesignal processing and control circuitry 10, any suitable criteria can beused to determine the beam directions for transmission. For example,other embodiments take into account minimisation of the generatedinterference in certain directions.

FIG. 5 thus illustrates a second embodiment in which pilot signal bitsof a communication burst are transmitted in serial fashion, each pilotsignal bit being transmitted at a particular time and in a differentdirection to the preceding pilot signal. The data signal bits for thatcommunication burst are subsequently transmitted in correspondingdirections and in the same order as the pilot signals. This embodimentis referred to herein as the time orthogonal pilot transmission (TOPT)method. The beams themselves may not be orthogonal. The width of thebeams may be alterable.

FIG. 6 illustrates a third embodiment which is a modified version of thetime orthogonal pilot transmission method, in which the pilot signalscorresponding to each direction are distributed throughout thecommunication burst. In the illustrated ith time slot, the pilot signalP is transmitted in three directions to define three pilot signal bitsP₁, P₂ and P₃. These three pilot signal bits are distributed evenlythroughout the slot and are each followed by a data block comprisingconsecutive data bits. According to FIG. 6, a first pilot bit P₁ istransmitted in the direction b₁ as is the subsequent data blockcomprising data bits d_(1N), d_(2N), d_(3N) to d_(NN). The second pilotbit P₂ is transmitted in a second direction b₂ and the next data blockcomprising data bits d_(1R), d_(2R), d_(3R) to d_(RR) is alsotransmitted in the direction b₂. Likewise, the third pilot bit P₃defines the direction of transmission for a third data block comprisingdata bits d_(1v), d_(2v), d_(3v) to d_(vv). There is three directionalhopping within the time slot of a single communication burst. Note,however, that the embodiment of FIG. 6 employs a slower rate ofdirectional hopping within a time slot than the embodiment of FIG. 5.

If the directions determined from the uplink communication direction arespatially orthogonal to each other, a fourth embodiment illustrated inFIG. 7 can be used. The determined directions are considered to beorthogonal if their angular separation between the beam maxima isgreater than about the one half power beam width. Assuming the radioenvironment carries a sufficiently large angular spread, then the use ofa conventional analogue beam former (e.g. butler matrix circuitry)achieves orthogonal antenna beam directions during both transmission andreception. The embodiment of FIG. 7 is referred to herein as a spaceorthogonal pilot transmission (SOPT) method. The pilot signal Ptransmission in the downlink direction involves the simultaneoustransmission of pilot signal bits P_(n) towards all of the determineddirections of transmission b₁, b₂ and b₃. Thus, the transmission ofpilot signal bits occurs at the same time and beam directions b₁, b₂ andb₃ are orthogonal. The subsequent data signal transmission D isperformed by employing different directions for consecutive data bitsbut in this case the order of transmission need not necessarily follow apredetermined directional transmission pattern, as was suggested withthe embodiment of FIG. 6. Here, the selection of directions fortransmission of data bits can follow any order, provided all of thedirections are defined by the pilot signal and are orthogonal. In thisexample, the selection of direction for data bit transmission is randomwith each direction b₁, b₂ and b₃ being used on average an equivalentnumber of times. This is possible because at the receiving mobilestation each received bit is convolved (correlated) with the channelresponse of the whole channel, including all of the directions involved.Since these directions are orthogonal to the received signal, theireffect will in principal be eliminated.

In a fifth embodiment illustrated in FIG. 8, a fixed number Np of pilotsignals are transmitted simultaneously towards the directions oftransmission to be used in the transmission of data bits within the samecommunication burst. The pilot signal for each direction has a uniquecode which is orthogonal to other codes being used in the pilot signaltransmission. Hence, this embodiment is referred to herein as codeorthogonal pilot transmission (COPT). Referring to FIG. 8, the pilotsignal bits P_(n) comprises three pilot signals having the spread codesC₁, C₂ and C₃ which are transmitted simultaneously in the directions b₁,b₂ and b₃. Thereafter, consecutive bits of the data transmission d₁, d₂,d₃, d₄ to d_(m) are transmitted in different directions and using thespreading codes defined for the particular direction concerned duringthe pilot transmission. The mobile station MS is able to estimateindividually the channel impulse responses corresponding to eachdirection and, as with the embodiment of FIG. 7, consecutive data bitscan be transmitted by the base transmitter station to the mobile stationMS in different directions using any directional transmission pattern,provided that when transmitting in the Nth direction, the associated Nthcode is used. The receiving mobile station MS will convolve theinformation of a given bit with the channel impulse response of thecomplete channel comprising all the directions of transmission used andtheir associated codes but, due to code orthogonality, only informationof the relevant transmitted bit is retained.

The performance of the various embodiments described leads toimprovements in correlations between the directions of arrival estimatedfrom the uplink communications and the selection of transmissiondirections for the downlink channels. Significant advantages include theprovision of fast angular diversity and the efficient whitening of thegenerated co-channel interference, particularly in multi-rate systems(e.g. W-CDMA and future wireless networks) in which high bit rate userstransmit with relatively high power levels and the conventional use ofadaptive antennas produces highly coloured spatial interference. Methodsembodying the invention have particular advantages in radio environmentscharacterised by large angular spreads (e.g. micro and pico cells) andwhen angular resolution of the base transceiver station is relativelyhigh. The performance of the method improves as the angular spread ofradio environment and spatial resolution of BTS increase. This isbecause as angular spread increases and the generated beams becomenarrower, the BTS can efficiently exploit the benefits of operating inthe spatial domain. For example, more hopping directions becomeavailable as these conditions are applied.

Embodiments of the invention can advantageously be used in micro and/orpico cells environments. Such radio environments not only carry largeangular spreads but are also characterized by small delay spreads due tothe small size of those environments. This is greatly beneficial,particularly in schemes exploiting orthogonality (e.g., codeorthogonality). It is also in these environments where high bit-rateuses can be expected. The level of co-channel interference generated toserve these users is reduced by employing methods embodying the presentinvention.

The quality of the channel estimation at the receiving mobile station MSis heavily dependent on the amount of energy used for transmitting thepilot signal bits. Since pilot transmission is multiplexed with respectto time-, space- and/or code domains, when the same energy as that usedin the conventional methods (slot-level processing) is distributed amongthe pilots, the effective energy per pilot is smaller. This degradationin the pilot signal power is compensated by the array gain.

The pilot and/or data signal transmissions within a communication burstmay be multiplexed with respect to time, frequency, space or spreadingcode. Methods illustrated with respect to pilot signal transmission canbe applied equally to data signal transmission. The different methodsdescribed hereinbefore can be used separately or in any combination.

Whilst embodiments of the present invention have been described in thecontext of a CDMA system, embodiments of the present invention can beused with any other type of access system. Embodiments of the presentinvention can be implemented in a mobile station as well as a basestation.

What is claimed is:
 1. A method of directional radio communication in awireless communications network between a first station and a secondstation, said method comprising the steps of: transmitting a pluralityof communication bursts from said first station to said second station,each of said bursts being substantially continuous and comprising areference signal having a plurality of reference signal components and adata signal having a plurality of data signal components, whereinrespective signal components of said reference signal are transmitted insubstantially different directions, the data signal components beingtransmitted in said substantially different directions, and wherein oneor more of said data signal components is transmitted before the lastreference signal component of the communication burst.
 2. A method as inclaim 1, wherein a number of said plurality of reference signalcomponents are transmitted in different directions at different times,successive reference signal components being transmitted in differentdirections.
 3. A method as in claim 1, wherein said reference signalcomponents are transmitted consecutively.
 4. A method as in claim 1,wherein a number of said plurality of reference signal components aretransmitted in different directions at substantially the same time.
 5. Amethod as in claim 1, wherein a number of said plurality of data signalcomponents are transmitted in different directions at substantially thesame time.
 6. A method as in claim 1, wherein a number of said pluralityof data signal components are transmitted in substantially differentdirections, at different times and consecutively.
 7. A method as inclaim 6, wherein consecutive data signal components are transmitted insaid different directions without regard to the order of directionaltransmission of said reference signal components.
 8. A method as inclaim 1, wherein said reference signal components are transmittedconsecutively, wherein a number of said plurality of data signalcomponents are transmitted in substantially different directions, atdifferent times and consecutively, and wherein the order of directionaltransmission of said data signal components corresponds to that usedduring transmission of said reference signal components.
 9. A methodaccording to claim 1, wherein said data signal components are dividedinto a plurality of sets, each set being transmitted after a respectivereference signal component.
 10. A method according to claim 9, whereineach set of data signal components is transmitted in the same directionas the preceding reference signal component.
 11. A method according toclaim 1, used in a code division multiple access system.
 12. A methodaccording to claim 11, wherein a different spreading code is used forthe transmission of respective reference signal bits in each direction.13. A method according to claim 11, wherein the reference signal is apilot signal.
 14. A method according to claim 12, wherein the spreadingcodes used in the transmission of said reference signal components insaid different directions are also used in the transmission of datasignal components in the corresponding directions.
 15. A transceiverstation for directional radio communication in a wireless communicationsnetwork between a first station and a second station, said transceiverstation comprising: means for transmitting a plurality of communicationbursts from said first station to said second station, each of saidbursts being substantially continuous and comprising a reference signalhaving a plurality of reference signal components and a data signalhaving a plurality of data signal components, said means being operableto transmit respective signal components of said reference signals insubstantially different directions, the data signal components beingtransmitted in said substantially different locations, wherein one ormore of said data signal components is transmitted before the lastreference signal component of the communication burst.
 16. A method ofdirectional radio communication in a wireless communications networkbetween a first station and a second station, said method comprising thesteps of: transmitting a plurality of communication bursts from saidfirst station to said second station, each of said bursts beingsubstantially continuous and comprising a reference signal having aplurality of reference signal components and a data signal having aplurality of data signal components, wherein respective signalcomponents of said reference signal are transmitted in substantiallydifferent directions, the data signal components being transmitted insaid substantially different directions, wherein said reference signalcomponents are transmitted consecutively, wherein a number of saidplurality of data signal components are transmitted in substantiallydifferent directions, at different times and consecutively, and whereinthe order of directional transmission of said data signal componentscorresponds to that used during transmission of said reference signalcomponents.
 17. A method of directional radio communication in awireless communications network between a first station and a secondstation, said method comprising the steps of: transmitting a pluralityof communication bursts from said first station to said second station,each of said bursts being substantially continuous and comprising areference signal having a plurality of reference signal components and adata signal having a plurality of data signal components, whereinrespective signal components of said reference signal are transmitted insubstantially different directions, the data signal components beingtransmitted in said substantially different directions, wherein a numberof said plurality of data signal components are transmitted insubstantially different directions, at different times andconsecutively, and wherein consecutive data signal components aretransmitted in said different directions without regard to the order ofdirectional transmission of said reference signal components.
 18. Atransceiver station for directional radio communication in a wirelesscommunications network between a first station and a second station,said transceiver station comprising: means for transmitting a pluralityof communication bursts from said first station to said second station,each of said bursts being substantially continuous and comprising areference signal having a plurality of reference signal components and adata signal having a plurality of data signal components, said meansbeing operable to transmit respective signal components of saidreference signals in substantially different directions, the data signalcomponents being transmitted in said substantially different locations,wherein said reference signal components are transmitted consecutively,wherein a number of said plurality of data signal components aretransmitted in substantially different directions, at different timesand consecutively, and wherein the order of directional transmission ofsaid data signal components corresponds to that used during transmissionof said reference signal components.
 19. A transceiver station fordirectional radio communication in a wireless communications networkbetween a first station and a second station, said transceiver stationcomprising: means for transmitting a plurality of communication burstsfrom said first station to said second station, each of said burstsbeing substantially continuous and comprising a reference signal havinga plurality of reference signal components and a data signal having aplurality of data signal components, said means being operable totransmit respective signal components of said reference signals insubstantially different directions, the data signal components beingtransmitted in said substantially different locations, wherein a numberof said plurality of data signal components are transmitted insubstantially different directions, at different times andconsecutively, and wherein consecutive data signal components aretransmitted in said different directions without regard to the order ofdirectional transmission of said reference signal components.